The early symptoms of chronic disease—such as Dyspnea, dizziness, and fatigue—are often mild and are common to many other conditions. At rest, there are often no symptoms and no apparent signs of illness. As a result, detection of the cause of dyspnea and the severity of the dyspnea can be delayed for months or even years. Accordingly, the presence of one or more chronic diseases is frequently not recognized until the disease is relatively advanced. A specific chronic disease is often diagnosed only once other conditions have been investigated and ruled out.
The non-specific nature of symptoms associated with chronic disease means that the diagnosis cannot be made on symptoms alone. Using pulmonary hypertension (PH) as an example, a series of investigations is required to make an initial diagnosis, to refine that diagnosis in terms of clinical class of pulmonary hypertension, and to evaluate the degree of functional and hemodynamic impairment. Current PH evaluation and classification (type, functional capacity, hemodynamics) methods include blood tests and immunology, HIV test, abdominal ultrasound scan, 6-minute walk test (6-MWT), peak VO2, right heart catheterization, and vaso-reactivity testing. It is with exercise in PH patients that the sympathetic and neuro-hormonal systems trigger increased vasoconstriction of the pulmonary arteriolar vascular beds, thus causing an elevation in pulmonary vascular resistance and reduced blood flow through the pulmonary vascular circuit. This response also increases the workload of the right heart during exercise. The reduced blood flow is mismatched to the air flow in the bronchioles and alveoli.
The World Health Organization (WHO) classifies pulmonary hypertension into distinct groups, including for example WHO Group 1 (“WHO 1”), WHO Group 2 (“WHO 2”), and WHO Group 3 (“WHO 3”), WHO Group 4 (“WHO 4”), and WHO Group 5 (“WHO 5”). Typically, the clinical differentiation of WHO 1 vs. WHO 2 or WHO 3 pulmonary hypertension, often termed primary vs. secondary PH, is confirmed by the invasive procedure of right heart catheterization (RHC) requiring the intravascular passage of a pressure monitoring catheter via the subclavian or cephalic vein into the right atrium, through the tricuspid valve and into the right ventricle with further maneuvering past the pulmonary valve and to the pulmonary artery (PA). The catheter is typically advanced further “downstream” in the PA with inflation of a distal tip balloon that occludes flow to allow for pressure monitoring of pressure on the pre-capillary side called a wedge pressure that has been reported to correlate well in most circumstance with left heart filling or left atrial pressures. The type of suspected pulmonary hypertension, whether true pulmonary arterial or venous hypertension is classified by hemodynamic criteria relative to the mean PA pressure and pulmonary wedge pressure values. The performing of a RHC imposes risk and often causes discomfort to the patient. Additionally, RHC is usually limited to gathering hemodynamic data while the patient is at rest without exertion due to the difficulties of supine patient exercise on the cath lab table.